Design Footing on Two Piles As Per ACI 318-99 Spreadsheet
Soil-cement is a mixture of soil and measured amount of cement, and water compacted at high density. They all together form a hardened mixture like concrete, under the hydration action of cement.
Soil cement is used to strengthen underlying soil conditions to support traffic loading. Cement stabilized base is also a common application to strengthen the base section directly underneath rigid or flexible pavements. Soil-cement can be used when paving roads, parking lots, airports, residential streets, and more. It’s a cost-effective pavement base known for its strength and durability.
Soil-cement is also called the cement-stabilized base, or cement-treated aggregate base.
It is primarily used as a base course for-
It is also used for:
First, rigorous laboratory tests are conducted to determine the cement and moisture content required to achieve the design compressive strength at a specific compactive effort. This analysis is then frequently referred to throughout the construction process to ensure that the soil-cement is of the highest quality.
Once the specific components of the mixture are decided, the material is mixed either in a central mixing plant or in-place. With central mixing plants, the soil-cement is first mixed and then brought to the job site. With in-place soil-cement construction, the mixing is done on-site. This involves first spreading the cement on the in-place soil. The cement, soil, and water are then mixed to a uniform consistency. During the final stages, the mixture goes through processes of compaction within a specified time limit and is cured. The curing process ensures that the soil-cement created is at its maximum strength.
Some soil-cement applications also require a process called “micro-cracking”. Micro-cracking of the soil-cement layer reduces the rigidity of the layer and the potential for cracking to reflect from the layer to the pavement.
Main processes involved in the construction of soil-cement are:
At the central mixing plant, mixing of the soil-cement mixture is done. The final mixture is then moved to the job site and laid over the already prepared sub-grade level.
Initially, a proper quantity of cement is being spread over the soil and mixed homogeneously. Then a measured amount of water is added and mixed thoroughly. The mixing can be done by hands or with mixing equipment or machines.
Now the compaction of the whole mixture is done by normally used compaction equipment. The compaction is done with high precision to achieve the maximum advantage of the cement used.
Once it is done, the whole mixture layer is cemented permanently at a very high density. After compaction, it won’t let the soil to undergo further consolidation or settlement under huge traffic.
The last step is curing. It is performed to prevent evaporation of water to the atmosphere. Proper cement hydration will be enabled only with an adequate amount of water. For this, a bituminous coating is laid over the layer and would act as a bituminous surface. The thickness of the layer can be increased if the pavement is constructed in an area with huge traffic.
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A buttress dam is also called as a hollow dam. It is a dam with a solid, water-tight upstream side that is supported at intervals on the downstream side by a series of supports. A reinforced concrete slab or a series of arches or thickened buttress heads may form the sloping membrane for retaining the upstream water. At the upstream end, a cut-off is provided to prevent or reduce the seepage of water.
A buttress is a thin wall of triangular profile shape. It has a characteristic of sloping upstream face. It is usually spaced at equal interval along the length of the dam and is supported either on a continuous mat foundation or on a separate spread footing. Each arch of the dam is supported by the buttresses. Multiple arch buttress dams are more durable and flexible than other buttress dams, such as a deck slab buttress dam.
The deck slab buttress dams are also known as Ambursen type buttress dams in honour of Nils F Ambursen who in 1903 built the first flat slab type of buttress dam. In this type of buttress dam, the sloping membrane or deck consists of a reinforced concrete slab supported by a series of buttresses. The inclination of the deck slab is kept between 40 to 55 degrees with the horizontal. In order to provide a wide base for the slab supported by the buttress the upstream end of the buttress where it joins the slab is usually made wide by providing haunch or corbel.
The deck slab buttress dam can be categorized into three types:
Each is having its own advantages and drawbacks. Advantage of the deck slab dam is that the deck slabs work together as a multiple arch dam for proper support. However, it is not like multiple arch dams, if one of the slabs gets damaged the damage will not affect the other slabs.
Buttress dams can be referred to as a gravity dam. The dam in which the concrete and material of the dam are designed to hold all the horizontal force and pressure of the water. Water pressure is distributed to the slabs of the Buttresses. Distributing the forces will reduce the load on the wall, allowing the dam to last longer.
In this type of buttress dam, the sloping membrane or deck consists of a series of reinforced-concrete arches supported by a number of buttresses. The upstream face of the dam is usually inclined at 45. The arches are cast monolithically with the buttresses. Multiple arch buttress dams are more durable and flexible than other buttress dams, such as a deck slab buttress dam. The dam can be constructed as a singular stiffened wall or a double hollow one. The biggest disadvantage of the dam is that buttresses depend on each other. It means that if one buttress develops problems the whole dam will lose its efficiency. This dam is suitable for larger heights preferably above 50 meters.
In this type of Buttress dam, the sloping membrane or deck consists of a series of reinforced-concrete domes supported by a number of buttresses. Most of the characteristics are the same as a multiple arch dam, however, instead of having arches it has domes. Using multiple domes help to reduce the number of buttresses required to make the dam stable. The main benefit is that the domes can be spaced farther apart than arches can be placed. It helps in reducing cost and saving material during designing of the dam.
The main feature of this type of dam is, there is no separate water-retaining member is provided and the water-retaining member is formed only by enlarging the upstream end side of the buttress. Thus the dam is made with a series of buttresses and massive heads placed side by side. They are constructed with concrete mass and little reinforcement. This makes its construction relatively easy compared to other types of buttress dams. The weight of the concrete makes massive head buttress dams very heavy, and very resistant to sliding.
This type of buttress dam does not have a slab or arch at the upstream face like other buttress dams. Instead of having slab at the upstream face, the massive head buttress dams have buttress heads that are extended and connected with other buttress heads. The larger buttress heads can be made in different shapes i.e. round and diamond. These extensions of the buttresses are made stronger by using copper strips in the construction. The massive head buttress dam is resistant to sliding because of its weight.
In this type of columnar buttress dam, the columns support the deck slab of the dam. The columns are inclined to the better support of the flat deck of the dam. The flat deck slabs are used to replace the buttresses. It is an altered deck slab buttress dam. It needs a very durable base. It requires skilled personnel to create buttresses. This is why it is not popular as much at the other types of buttress dams.
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Wind Load on Roof Screen Based on IBC 2006 / ASCE 7-05